Recently, with an increase in the amount of polyolefins being produced, there has been a tendency toward a large volume polymerization reactor to be employed or to increase the amount of polyolefins being produced per polymerization reactor. For heat removal from the polymerization reactor, therefore, various methods as well as the usual heat removal method using a jacket have been developed, including a method in which an internal cooler (e.g., a plate cooler, a coil cooler, etc.) is mounted in the polymerization reactor, and a method in which a reflux condenser is used for the heat removal by circulating a liquid phase portion in the polymerization reactor into an external cooler. Such a method using the reflux condenser is described in British Pat. No. 991,397, U.S. Pat. Nos. 3,785,430 and 4,061,848, etc.
The method using the reflux condenser, however, suffers from the disadvantage that when the reflux condenser is continuously used, active catalyst particles and polymer particles, both of which particles are entrained in gas to be condensed, deposit on the heat transfer surface of the reflux condenser to form scales such as films, bulk materials and the like of polymers, which results in a reduction of the heat removal ability. Furthermore, these scales give rise to various problems, that is to say, when they are locally stripped off, they clog a flow path through which the condensed liquid returns to the polymerization reactor, enter the polymerization reactor to adversely affect the quality of polyolefin products, and clog a conduit through which the liquid phase portion in the polymerization reactor is withdrawn. In order to remove such problems, it is necessary to wash the heat transfer surface of the reflux condenser at about 2 or 3 month intervals.
For washing the heat transfer surface, it is necessary to separate the reflux condenser from the polymerization reactor by stopping the polymerization or by reducing extremely the amount of polyolefins being produced. This leads to a marked reduction in productivity.